Continuous and incremental photographic film printers have been used which include both notch and RF systems for automatically controlling the light valves of the printer to vary the intensity and hue of the light for the scene being printed. These devices have some inherent disadvantages because the mechanical pickups which engage film notches would damage the film if the printer were operated at too fast a speed. The patcher used on the film strip in the RF system tended to fall off or get lost particularly during clearing of the film.
This invention relates to an apparatus for controlling the operation of a photographic film printer, and more particularly relates to an apparatus for reading a scene length tape to automatically control the light valves of such a printer so as to provide intensity and hue correction for the scene being printed and to permit operation of the film printer at a significantly higher speed.
During the operation of a film printer, an unexposed film or "raw stock" is placed in an overlying relation to a "preprint" film for contact printing. The "preprint" film and the overlaid "raw stock" are in sprocket hole registration and driven by a single sprocket wheel across an aperture for exposure by a controlled light source. The "raw stock" thus is exposed in accordance with the image of the "preprint" film and thereafter developed by conventional methods. Various scenes of the "preprint" film which make up the complete film are frequently photographed at different locations and under varying lighting conditions. Therefore to minimize or eliminate the lighting and color variations which occur as a result of variations in lighting during the initial filming, each of the scenes of the "preprint" film often require different optimum printing levels and color balance during exposure of the raw stock. Prior to the exposure of the "raw stock", the "preprint" film is visually inspected by a skilled operator for the purpose of determining the intensity and hue of the correction desired for each scene. According to the conventional practice, lighting correction for each scene is recorded by punching a paper tape. During printing, the film printer utilizes and reads the punched tape to control the light valve of a variable light source focused upon the printer exposure aperture.
The length or position of the scene to which the light setting relates is similarly recorded on a second punched tape in a binary coded decimal (BCD) code. This information may be in the form of a film length measure starting at the termination of the last scene and is termed hereinafter the "batch" method of scene length measurement. Alternatively, the information may be in the form of a film length measure starting at a predetermined starting position on the film such as a punched "sync hole" and is termed hereinafter the "milestone" method of measuring scene position.
Therefore, during the initial viewing of the master "preprint" film, the operator punches two tapes, a first recording the scene light level and color correction desired, and a second recording the scene length to which the correction corresponds following either the "batch" or "milestone" methods of scene length measurement. The use of separate scene length and light control tapes is particularly convenient since this combination readily adapts to practices presently in use. The conventional methods using the notch or RF systems require the operator of a photographic laboratory to punch a first tape carrying the lighting intensity information for control of the light valves and apply notches or magnetic patches to the film indicating the location of a scene change. As will be described hereinafter, in lieu of notching or patching, the operator can more conveniently punch a second tape carrying scene length information thus making the illustrated embodiment totally compatible with the present laboratory practices.
As previously described, the "preprint" film and "raw stock" film are in sprocket hole registration and driven through the printer in an overlying position. A pulse generator provides an output signal relating to the amount and direction of film driven across the exposure aperture. The actual film travel then is compared to the scene length information recorded on the scene length tape, and when the two sources of information coincide, a cue signal is generated. The cue signal actuates the light valves causing them to attain the desired lighting and color correction for the scene being printed. The light printing level and color correction are adjusted between each scene upon command in accordance with the recorded tape information.
A suitable light source for use with the illustrated embodiment is shown in U.S. Pat. No. 3,502,409, assigned to the assignee of the present invention, and includes dichroic mirrors which serve to separate a spectral light source into three primary color light beams. Further details thereof are incorporated by reference herein. However, suffice it to say that three light valves, each of which relates to a primary color, are adjustably set to control a selected portion of the light in one of the primary color beams. Each light valve includes a movable vane which intercepts a primary color beam and a bar-type adder unit having a plurality of solenoid actuated slides wherein the desired vane position is stored. Signals from the light valve tape representing the selected intensity and hue correction factors are applied to the slide solenoids causing the adder unit to expand linearly by an amount corresponding to the correction desired. The information in the bar-type adder unit is converted to an angular rotation of a vane memory and stored therein. The angular position of the vane memory is transferred to the vanes upon receipt of a cue signal by actuating a vane solenoid which in turn moves a vane into the path of the primary color beam of an amount determined by the angular position of the vane storage memory. Therefore, in response to a cue signal, the lighting information stored in the valve is transferred to its respective vane and the valve is cleared to receive the lighting information corresponding to the next scene to be printed.
Previous frame count cuers have suffered from several design problems. Particularly, direct electrical connection with the film printer often has caused or permitted small electrical signals (noise) to be transferred from the film printer to the cuer which can interrupt the logic of the cuer. It also is desirable to have the frame count cuer operate in a reverse direction to avoid the necessary rewinding of the "preprint" film after each printing operation or alternatively to permit continuous or "loop" printing of a short subject whose film length is several times smaller than that of a conventional "raw stock" reel of film. It also is desirable to include a method for advancing the cue signal a predetermined number of frames to allow for the time delay caused by the light valve memory and solenoids. For convenience of tape preparation and bi-directional operation the scene length is coded with the information related to the film scene, which information is thereby varied by the cue advance unit to provide advanced or delayed cue signal generation.